Even by the freewheeling, mood-swinging standards of Bollywood, the pronounced disparity between the pre- and post-intermission halves of "Jab tak hai jaan" is more than a tad jarring.

Even by the freewheeling, mood-swinging standards of Bollywood, the pronounced disparity between the pre- and post-intermission halves of “Jab tak hai jaan” is more than a tad jarring. Indeed, viewers may feel they’ve been treated to an oddly matched double bill — a delightfully vivacious romantic dramedy, followed by an Old Hollywood sort of psychological melodrama — by the time the closing credits roll. And yet, almost miraculously, the disparate elements add up to an improbably entertaining hybrid, one that, judging from opening weekend grosses in India and North America, ticketbuyers will have no difficulty accepting.

To be sure, some of the pic’s early B.O. success (on the subcontinent, at least) may be attributable to its cachet as the final completed work of Bollywood icon Yash Chopra, the prolific producer-director who died Oct. 21 at age 80. (Photos and footage of the late filmmaker are respectfully displayed during the opening and closing credits.) But even auds unfamiliar with Chopra’s career — indeed, even viewers uninitiated with the intoxicating excesses of Bollywood cinema — likely will find much to enjoy in this spirited masala of music and emotions.

Opening scenes strike a mildly portentous note while introducing Indian army officer Samar Anand (Shah Rukh Khan) as a coolly proficient bomb defuser in Ladakh whose utter lack of regard for personal safety might seem excessive even to the adrenaline-junkie protagonist of “The Hurt Locker.” Samar has earned the title “the Man Who Cannot Die” after a long string of successful missions. Right from the start, however, it’s clear he’s at least partly motivated by a death wish.

The mood brightens appreciably when Samar meets cute with Akira (Anushka Sharma), a spunky Discovery Channel intern and would-be documentarian who fortuitously takes a swim near a beach where Samar is enjoying some R&R. He rescues her from drowning, but doesn’t stick around long for thanks.

Before zipping off on his motorcycle, however, Samar chivalrously leaves the dripping damsel his jacket. And wouldn’t you know it, Akira just happens to find his diary in a jacket pocket, and spends the next hour or so reading about Samar’s carefree days as a waiter and street musician a decade earlier in London.

That’s where we see him enthusiastically wooing Meera (Katrina Kaif), a wealthy but reticent beauty who loosens up quite a bit after they engage in a “Step Up”-style dance-off, one of several full-tilt production numbers set to the pulsating music of Bollywood mainstay A. R. Rahman.

Scriptwriters Aditya Chopra (the director’s son) and Devika Bhagat borrow a page from Graham Greene’s “The End of the Affair” to delay the couple’s happily-ever-aftering. Post-intermission, there’s some residual playfulness in the plotline as Akira, now hopelessly smitten with Samar, contrives to document his bomb-defusing exploits for the Discovery Channel. She manages to overcome his gruff emotional reserve, leading to a sweetly loony scene that has them dangling from a bridge and swapping jokes while he figures out which IED wire to cut. But when Samar visits London to confirm details in Akira’s doc, “Jab tak hai jaan” takes an abrupt turn into very serious, even soap-operatic territory.

Thanks in large measure to the appealing sincerity of the three lead performances, the film remains rooted in some semblance of emotional truth even as its multiple contrivances and vertiginous tonal shifts veer perilously close to absurdity. Khan is particularly impressive in the way he maintains his equilibrium during the story’s vacillations between exuberance and intensity, and he’s persuasive whether his character is dicing with death or dancing with joy.

Kaif is most effective during the pic’s second half, in scenes that emphasize Meera’s deeply felt fear that she may drift from God if she follows her heart. Sharma is borderline exhausting in her sprightliness, but more often than not, and especially when she swirls and shimmies while singing an uninhibited ode to “falling in love with myself,” she, like the pic itself, is well-nigh impossible to resist.